This is generally a CD mechanism malfunction.
There are a couple options really, the first would be to try a battery disconnect to make the CD mechanism reset itself and see if that works.
If that does not work, then you need to manually remove the CD. One thing that works well that most people have at their house is a small putty knife used for sheetrock/painting etc. You just tape the edges of it and use it to fish out the CD. I have done this before and found where people have forced multiple discs in the slot as well and it still work.